ix PLATYSTERNIDAE TESTUDINIDAE 345 



nail-like horny point. The lobes of the plastron are well hinged 

 in the adult. 



C. leucostomum of Central America is larger, with a shell-length 

 of six inches. The plastron is not at all cruciform, but has a 

 broad bridge, and fills the box, moreover it has an anterior and a 

 posterior hinge, so that the box can be completely closed. Hence 

 the vernacular name of the Box-Terrapin. 



Fam. 4. Platysternidae, represented by the single species 

 Platysternum megaceplialum in Burma, Siam, and Southern China. 



The pectoral shields are widely separated from the marginals 

 by inframarginals, the plastron is large, oblong, not cruciform, 

 and the tail is long. 



The plastron consists of nine plates, and is covered with six pairs 

 of shields, the most anterior of which are the broad gulars. The 

 nuchal plate has no rib-like processes. The neurals form a con- 

 tinuous series, and there are twenty-three marginal scutes. The 

 temporal fossae are completely roofed over, owing to the long sutures 

 formed by the parietals with the postfrontals, moreover the post- 

 frontals expand laterally so much that they posteriorly come into 

 broad contact with the quadra to-jugals and squamosals, anteriorly 

 with the maxillaries, so that the jugals are completely surrounded 

 by bones, and are shut off from the orbits and from the temporal 

 fossae. This is a unique arrangement, found nowhere else in 

 Tortoises. The pubic and ischiadic symphyses are connected 

 with each other by ligaments only. 



The general appearance of this water-tortoise is rather curious, 

 since the carapace is much depressed, looking, especially in 

 younger specimens, as if it had been crushed in. The head, pro- 

 vided with very strong hooked jaws, is strikingly heavy and 

 large, and is covered above with one single large shield. The tail 

 is longer than the shell, which, in full-grown specimens, reaches 

 about six inches in length ; it is, throughout its length, covered 

 with rings of squarish shields. A large specimen measures 14 

 inches in total length, of which only five fall to the shell. 



Fam. 5. Testudinidae. The shell is always covered with 

 well-developed horny shields. Those which form the plastral 

 bridge are in direct contact with the marginals. The plastron is 

 composed of nine bones. The digits have four or five claws. 

 The neck is completely retractile. The skull is devoid of parieto- 

 squamosal arches. 



